A Flow Network Modeling (FNM) Tool MacroFlow TM for Improving Productivity of the Design of Complex Flow Systems Kanchan

1. A Flow Network Modeling (FNM) Tool MacroFlowTM for Improving Productivity of the Design of Complex Flow Systems Kanchan M. Kelkar, Ph. D. Principal Engineer kelkar@inres.com

2. Outline • Overview of the Design Process and the Role of FNM • Theory of FNM • Demonstration of MacroFlow • Validation of FNM Results • Applications and Case studies • Hands-on Session

3. Typical Challenges in the Design of Complex Flow Systems • Blower/Pump Sizing • Flow Balancing • Filter Degradation • Bypass Effect • Manifold Maldistribution • Valve Selection • Minimizing Pressure Loss • Tube Sizing • etc.

4. The technique of Flow Network Modeling (FNM)as incorporated in MacroFlow enables you to analyze many design options accurately in a very short time.MacroFlow is a productivity tool. Objective of the Presentation

5. Real System – Exhaust System of a Dump Truck Flow Network Modeling is the only feasible technique

6. Modeling Options for System Design • Hand Calculations (HC) • Tedious and very limited • Spreadsheets (SS) • System-specific, inflexible, and time intensive • Flow Network Modeling (FNM) • Simple, fast, and accurate • Computational Fluid Dynamics (CFD) • Time intensive for model definition, solution, and postprocessing • Suitable for component analysis, not suitable for system-level design

7. What is Flow Network Modeling? • Flow systems are like electrical circuits. • Just as a voltage drop drives a current, a pressure drop creates fluid flow. • The flow distribution through different flow paths depends upon their flow resistances. • A flow system can be represented as a network of flow resistances. This approach is called Flow Network Modeling (FNM).

8. A Network for a Piping System

9. FNM of Complex Flow Systems • A network model of the flow system is constructed by identifying flow paths through filters, screens, bends, tees, blowers/pumps, valves, orifices, etc. • The flow resistance relationships can be obtained from handbooks, vendor specs, in-house testing, or CFD analysis. • The flow rates, pressures, and temperatures throughout the system are calculated by solving mass, momentum, and energy equations.

10. Advantages of the FNM Technique • FNM is simple, fast, and accurate • Simple because it is modular and object-oriented • Fast because it uses overall characteristics • Accurate because characteristics are empirically determined

11. Limitations of FNM • The flow system must be described in terms of identifiable flow paths with definable resistance characteristics. • FNM provides gross (rather than detailed) predictions: • FNM solution does not give local velocity vectors, flow separation, reattachment, etc. • Detailed temperature distributions, local heat fluxes, etc. are not calculated. • Accurate resistance correlations are needed for reliable prediction.

12. Complementary Nature of FNM and CFD • FNM allows focused and efficient use of CFD • Examine hundreds of design alternatives by FNM (Conceptual Design) and select a few promising designs for CFD analysis (Detailed Design). • Use FNM for an entire system and provide boundary conditions for the CFD analysis of a subsystem. • Use of CFD at the component level for determining the flow resistances enhances the accuracy of the to the FNM technique. • Complementary use of System Analysis and CFD results in • A comprehensive set of tools for complex flow systems. • Shorter design cycle

13. Time Required to Analyze a Typical System Setup Time Run Time FNM 1 Hour 10 Seconds By using FNM, you save a substantial amount of design engineer’s time

14. HC Testing FNM CFD Testing FNM Testing Thermal Design Process Conventional and Enhanced Conventional Test-Based Enhanced FNM-Based

15. 2 1 Modified Bernoulli’s Equation For constant density and no gravity head: p1 + V12/2 = p2 + V22/2 + Losses The losses are due to viscous forces, flow separation, expansion/contraction, bends, etc. Losses = K(V2/2)where K is the loss coefficient. Thus, P = P1 - P2 = K(V2/2)

16. Flow Resistance P = P1 - P2 = K(V2/2) Q = VA  P = K( Q2) / (2A2) Flow resistance: P /Q = (K Q) / (2A2)(nonlinear) • The values of K are available for screens, orifices, bends, expansion/contraction, T-junctions, etc. • For electronics cooling, the K values are needed for card arrays, heat sinks, power supplies, etc.

17. Flow Resistance Flow resistance correlations for various flow geometries are given in: • Idelchik, I.E., Handbook of Hydraulic Resistance, CRC Press, Florida, 1994. • Blevins, R.D., Fluid Dynamics Handbook, Krieger Publishing Company, 1984. • Miller, D.S., Internal Flow Systems, Gulf Publishing Company, Texas, 1990.

18. Flow Resistance of a Duct p2 Friction factor: f = p (D/L) / (V2/2) Thus, K = f L/D • For duct flows, f is a well-established function of the Reynolds number Re and surface roughness. Re = VD/, where  = viscosity and D = hydraulic diameter = (4)(area)/perimeter p1 D L

19. Flow Through an Area Change (The color shows total pressure) • For an abrupt expansion: K = (1 - A1/A2)2 • For an abrupt contraction: K = 0.5 (1 - A2/A1)

20. p Qmax Q Flow Induced by Fans • Whereas flow resistances cause a drop in pressure, a fan creates a rise in pressure. • The pressure rise p produced by a fan depends on the flow rate Q. • This relationship is expressed by the fan performance curve.

21. system resistance fan curve p operating point Q System Operating Point • What flow rate we get is determined by the intersection of the system resistance and fan performance curves. • If the resulting Q is not acceptable, you reduce the system resistance, choose a different fan, or use multiple fans in series or parallel.

22. Ta2 Ta1 h1 h2 A B C Overall Thermal Resistance • For heat transfer through a composite solid from the hot fluid at Ta1 to the cold fluid at Ta2 Overall Resistance = 1/h1A + (L/kA)A + (L/kA)B + (L/kA)C + 1/h2A Heat flow: q = (Ta1 - Ta2)/ overall resistance q

23. Heat Transfer in FNM • Solve the flow equations to get the flow rates through individual components. • For a known heat load in a component: • Calculate the exit fluid temperature as: Tout = Tin + (q / mcp ) • Use a suitable correlation to get the heat transfer coefficient h for the calculated flow rate. • Then calculate Twall from: (Twall -Tout) / (Twall -Tin) = exp (- hA /mcp ) • •

24. Heat Transfer in FNM (continued) • For heat loss from the fluid within a component to the ambient fluid: • Calculate the overall heat transfer coefficient U as: U = [(1/hinside) + (L/k)wall + (1/houtside)]-1 • Obtain the exit fluid temperature from: Tout - Tamb = (Tin - Tamb) exp (- UA / mcp ) • Get the heat loss as: q = mcp (Tout - Tin) • •

25. FNM for System Design • FNM empowers the design engineer • to visualize the flow behavior of the entire system • to predict system-wide effects of a design change • to identify performance-limiting components • to quickly evaluate different physical layouts • to explore many available design options • to perform “what-if” studies • to avoid costly design changes later in the cycle • to meet tight design schedules

26. MacroFlowTMA Flow Network Modeling Tool for the Design of Flow Systems

27. Capabilities of MacroFlow • An integrated and easy-to-use GUI for network construction, solution control, and display of results • A comprehensive component library for modeling complex flow systems • Customizable and expandable structure • Robust and efficient direct solution technique • Steady/unsteady, Incompressible/compressible flow and heat transfer • Input and output in mixed units • Comprehensive post-processing in terms of plots, tables, animation

28. MF Demonstration of MacroFlow • Ease of use • Speed of execution • Flexibility and user control • Expandable and customizable structure • Tool for enhanced productivity

29. Flow through an “S” Manifold

30. Flow through an “S” Manifold Comparison with Experimental Data

31. Flow through a “U” Manifold

32. Flow through a “U” Manifold Comparison with Experimental Data

33. Exhaust System of a Dump Truck – Physical System

34. Exhaust System – The Design Problem Design Goals: • Minimize the back pressure while recovering waste heat Technical Approach: • Large size and widely different length scales made CFD analysis of the entire system impractical • Use of MacroFlow at the system level and CFD for localized analysis of complex regions

35. Exhaust System – Flow Network Model

36. Exhaust System – Design Cycle • MacroFlow-based analysis indicated regions of system with large pressure losses. • CFD analysis was used to optimize the local geometry (e.g. gradual expansion instead of a sudden expansion) and to determine the flow characteristics for use in MacroFlow. • The final design met the stipulated backpressure requirements. • MacroFlow enabled scientific analysis during the design process and resulted in an order-of-magnitude reduction in the associated costs.

37. Liquid Cooling System for Automatic Test Equipment Manifold System Liquid Cooling Module

38. ATE System – The Design Problem Design Goals: • Achieve a uniform distribution of flow to each LCM Design Iterations: • Selected the tube sizes for the main and the side branches • Determined the orifice sizes in the individual branches for flow balancing • Sized the pump for the cooling system

39. Liquid Cooling System – Characteristics of One LCM A Single LCM Flow Characteristics

40. Liquid Cooling - Flow Network Model for the Complete System

41. Liquid Cooling System – Distribution of Flow rates in One Branch of the Manifold

42. Why use MacroFlow? • Each design option can be analyzed very quickly and accurately. • Further, 80% of the design problems can be analyzed in 10% of the time relative to conventional techniques. • Complementary use with CFD results in a powerful design methodology. • The resulting cost savings and the quality improvements far outweigh the investment in MacroFlow usage.

43. Engineering Applications of MacroFlow • Electronics Cooling • Telecommunications • Computer • Avionics • Peripheral Equipment • Semiconductor Processing • Gas and Liquid Distribution Systems • Automobile • Intake and Exhaust Manifolds • Engine Cooling Systems

44. Closing Remarks • Flow Network Modeling is a simple, fast, and accurate methodology for the design of complex flow systems. • The promise of FNM is delivered by MacroFlowthrough its ease of use, flexible and customizable structure, speed of execution, and comprehensive post-processing. • Use of MacroFlow substantially shortens the design cycle and significantly improves the productivity of the design engineer.